Over the past year, this laboratory and others have identified, purified, and N-terminally sequenced a novel class of PTH-like proteins (PTHLPs) which appear to be responsible for humoral hypercalcemia of malignancy (HHM). The structure, location and transcriptional pattern of the PTHLP gene has been elucidated. Further PTHLPs and their mRNAs have been identified in a variety of normal, non-malignant tissues. It has been demonstrated that parathyroid hormone (PTH) also induces functional responses in a variety of tissues which have no obvious role in mineral homeostasis. The recent demonstrations that: a) PTHs are expressed by a spectrum of normal tissues including some of the "non-classical" PTH target tissues, and that b) PTHLPs interact with "classical" PTH receptors in bone and kidney raise the possibility that the receptors in these "non- classical" tissues are in fact PTHLP receptors. Finally, preliminary evidence suggests that differences may exist between "PTH receptors" in bone and kidney. Specific proposals now include to: 1) Comprehensively evaluate the possibility that there are subtypes of PTH receptors in bone as compared to kidney. Binding kinetics and adenylate cyclase responses of PTH and PTHLP will be examined in human and rat bone and kidney membranes. 2) Pharmacologically and structurally characterize the putative PTHLP receptors in the following :non-classical" target tissues: vascular smooth muscle, brain, and epidermal keratinocytes. 3) Compare transmembrane signaling mechanisms employed by PTH and PTHLP receptors in "classical" and "non-classical" target tissues, including adenylate cyclase, cytosolic calcium, and inositol phosphate turnover. Further knowledge of PTH/PTHLP receptors will help to characterize the patho-physiology of HHM, to elucidate the physiologic roles for PTHLP, and to design PTH/PTHLP agonists/antagonists for treatment of hypercalcemia and the management of osteoporosis. The candidate has gained experience in many of the techniques required to conduct the proposed studies including receptor-binding assays and data analysis, photoaffinity crosslinking, polyacrylamide gel electrophoresis, autoradiography, radioiodination ofpeptides, and reverse-phase HPLC. Through the stimulating environment of Dr. Stewart's laboratory at the West Haven VA Medical Center and the close interaction with Dr. Broadus' and Dr. Rasmussen's laboratories at Yale, the candidate's technical and intellectual abilities will expand and mature in the future. Finally, the candidate has demonstrated an enthusiastic commitment to a career in academic medicine.